It is often desirable to produce light which is controlled to produce a constant and stabilized output. It may be challenging to control simple semiconductor light sources, such as light emitting diodes (LEDs), using simple circuitry.
According to the present system, a simple circuit is described which obviates many of these problems. The circuit uses a semiconductor light source and a semiconductor photoreceptor within the feedback loop of a controlled amplifier. The amplifier can be an operational amplifier which uses the light source and photoreceptor within its feedback loop. The photoreceptor senses a level of the illumination light, and the operation of the feedback loop maintains that illumination light constant at a desired level. In an embodiment, the illumination light may be varied according to a digital control.